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Research Highlights
Improving Roots Improves Soybean Yields

Growing test soybeans in pots in controlled laboratory conditions allowed the team to evaluate the impact of each of the potential “root genes” on plant growth.

By Laura Temple

Roots are the foundation of a crop. They make water and nutrients available to the plant. Soybeans need strong roots to maximize water use, defense and plant nutrition.

“Root biology is often getting less attention because it is harder to study than the portion of plants above ground,” says Dr. Neal Stewart, professor in the Department of Plant Sciences and co-director of the Center for Agricultural Synthetic Biology at the University of Tennessee Institute of Agriculture. “Yet improved crop yield and characteristics like drought tolerance are impossible to achieve without strong root systems.”

How can soybeans develop stronger root systems? 

Stewart’s lab has been investigating “root genes” in soybeans to increase root length and branching to boost yield and resiliency. The Tennessee Soybean Promotion Board is funding this research. The research team from Stewart’s lab is led by Research Scientist Mitra Mazarei and Associate Professor Tarek Hewezi.

“Root system architecture roughly mirrors the plant above ground, with both vertical and lateral branches,” Stewart says.

Deep, vertical roots allow soybeans to reach the relatively stable source of water in deeper soil layers. Shallow, lateral roots increase the potential absorption surface area in the topsoil, where nutrients accumulate. Soybeans need both types of roots to improve water and nutrient update efficiency.

“Based on our fundamental knowledge of roots, we started the gene discovery process to improve them in soybeans,” he explains. “We looked through translational literature for information about genes that control root growth in other plants. Then our team looked through the sequenced soybean genome for similar genes with the potential to control root branching and vertical growth.”

Root Gene Discovery

After identifying about 10 genes potentially associated with root growth and development, the team used hairy root assays, a test process for early stages of gene discovery, to identify the best candidates for further research. Soybean roots were genetically engineered to over-express several of these genes one at a time. 

In these lab-grown hairy root assays, some test results showed roots nearly twice as long as the control, Stewart reports. Others grew root masses between 60 and 70 percent greater than the control. Based on these results, his team identified the three most promising genes for in-depth study. 

Soybean plants with genetically engineered hairy roots overexpressing the individual candidate genes were grown to full maturity in a greenhouse. Growing these soybeans in pots in controlled laboratory conditions allowed the team to evaluate the impact of each of the potential “root genes” on plant growth and seed production, including biomass weight, flowering time, pod setting, seed count and seed weight.

“We could see the difference between root systems in the pots,” Stewart reports. “Our initial results show potential for yield increases. We expect that will translate to potential to improve drought tolerance and ability to handle other stresses in the field.”

The next step was to stably insert these genes into a research soybean line, which was the team’s focus in 2020. The research team is continuing to evaluate these three genes while developing more seeds that strongly express them. Assuming the lab results continue to show promise in the stably transgenic soybean line, the team plans to run a field experiment in 2022 to see how these genes influence root development and water use in real-world conditions.

Stewart notes that because these are soybean genes, they plan to use genetic tools with minimal regulatory burdens to make soybeans with better root genetics available to farmers more quickly. 

“We expect that our discovery and identification of novel root-important genes will lead to the production of soybeans with deeper, more extensive root systems,” Stewart says. “Our study will provide a basis for development of soybean lines with improved growth and tolerance to abiotic stresses. These soybeans will have improved performance and yield, particularly under conditions with limited water and nutrient availability.”

Casey Youngerman farms near Lexington, Tenn., and serves as chairman of the Tennessee Soybean Promotion Board. He reinforces the value of this checkoff-funded research. “Dr. Stewart’s research solves problems and looks for innovations to help soybean farmers here in Tennessee,” he says. 

To find research related to this Research Highlight, please visit the National Soybean Checkoff Research Database.